I needed a grille for an air vent in a non standard size. Here's a parametric model in OpenJsCad.Go to http://joostn.github.com/OpenJsCad/ Scroll down to Examples and choose Parametric Grille. The size and some other parameters are customizable. Click Generate STL and Download STL to get your custom grille. Or you can download the jscad file and process it in the OpenJsCad parser: http://joostn.github.com/OpenJsCad/processfile.html